The Deep Soil Mixing Method (DSM) is a soil stabilization technique by which soil-cement walls or columns are formed in situ. The DSM method is practiced by the use of a crawler crane having a set of leads which guides a plurality of hydraulically driven mixing paddles and augers. The hollow stemmed augers penetrate the soil, and a grout slurry is injected into the soil through the auger tip. As the auger flights break up the soil, it is lifted to the mixing paddles where it is mixed with the grout as the auger continues downward and is subsequently withdrawn. The augers are next moved adjacent to and overlapping the first excavation and the procedure is repeated, so that a selected pattern of continuous soil-concrete walls is formed. Vertical reinforcing beams are often placed into the soil-concrete structure to increase bending resistance.
The DSM method is used to form soil-cement structures for excavation support walls, such as for tunnels, retaining walls, water cutoff walls, foundations, and the like. In addition to construction, the DSM method finds usefulness in soil stabilization, environmental remediation, backfilling and landfill applications.
A problem that is encountered, however, by the DSM method, is the difficulties encountered with highly cohesive soils, such as fine sand, silty soils and clay. An example of this is Boston Blue Clay, a glacial clay deposit that is very cohesive. The auger has difficulty augering into the soil, which is primarily this cohesive clay, to permit the introduction of a cement grout.
There are known disperants for clay, particularly bentonite clay, used in oil well drilling and some construction techniques. However, these are primarily useful for aqueous slurries carrying a small percentage of clay (5-10%) as a dispersion with water as the continuous fluid. In the DSM method, the continuous phase is the soil, containing about 25% water in a form that is primarily bound within the clay layers. These bentonite aqueous dispersants are useful for low concentrations of the clay in water, used to carry rock cuttings away from the drill bit. They are not useful in enhancing the workability of soil in the DSM method.
Another drawback of conventional clay dispersants with respect to the DSM method, is that when added to the soil, they cause immediate flocculation, or setting of the cement grout when it is contacted with the dispersant-soil mixture. This prevents thorough mixing of the cement grout with the soil which is needed so that uniform strength can be developed, and further prevents reinforcements from being placed into the soil-cement structure.
It is therefore an object of the present invention to provide a deep mix soil stabilization method which enhances workability of highly cohesive soils, such as fine sand, silty soil and clay.
It is also an object of the present invention to provide a deep mix soil stabilization method which enhances workability of highly cohesive soils, such as fine sand, silty soil and clay by the use of soil dispersants.
It is a further object of the invention to provide a deep mix soil stabilization method which avoids premature flocculation of the soil and cement grout mixture to permit thorough mixing of the soil and grout and the introduction of reinforcements into the soil-cement structure.
It is a further object of the invention to provide a deep mix soil stabilization method which uses soil dispersants which do not cause premature flocculation of the soil and cement grout mixture to permit thorough mixing of the soil and grout and the introduction of reinforcements into the soil-cement structure.
It is a further object of the invention to provide a deep mix soil stabilization method which provides lower viscosity of the soil-cement mixture, and enhances compressive strength development of the stabilized soil-cement structure.
It is a further object of the invention to provide a deep mix soil stabilization method which provides lower viscosity of the soil-cement mixture, and enhances compressive strength development of the stabilized soil-cement structure by the use of cement dispersants in combination with the soil dispersants.
These and other objects of the invention are accomplished by the method which is hereafter described and claimed.